Xerographic fusing apparatus



C. F. CARLSON XEROGRAPHIC FUSING APPARATUS Feb. 26, 1963 4 Sheets-Sheet 1 Filed Dec. 5, 1956 T N E B m s B A INVENTOR. CHESTER F CARLSON VE NT Feb. 26, 1963 c. F. CARLSON 3,078,539

XEROGRAPI-IIC FUSING APPARATUS Filed Dec. 5, 1956 4 Sheets-Sheet 2 S LV E NT ABSORBENT sol-VENT ABSORBENT HEAT COL D SOLVENT SOLVENT ABSORBED SOLVENT VAPOR IN IMAGE VAPOR HEAT FROM ROOM HEAT To ROOM AND AB5OR5ENT COLD N ABSORBENT+ AND OR HEATER SOLVENT Elsi BATH TO SOLVENT t RECLAIMING l COLD SOLVENT SPENT SOLVENT VAPOR ABSORBENT 1 H01- HEAT E 7 ABSORBENT HEAT INVENTOR. CHESTER F. CARL SON HEAT Feb. 26, 1963 c. F. CARLSON 3,078,589

XEROGRAPHIC FUSING APPARATUS Filed Dec. :s, 1956 4 Sheets-Sheet s ELECT RO PRI NTING MPCHI NE 14'; 154' (9 gggmg A EL MACHINE 0 9 J 9 INVENTOR. CHESTER F. CARLSON Feb. 26, 1963 c. F. CARLSON 3,078,589

XEROGRAPHIC FUSING APPARATUS Filed Dec. 3, 1956 4 Sheets-Sheet 4 XEROGRAPHIC CONTINUOUS WEB MACHINE .1 r J v 522 520 XEROGRAPHIC 2% commuous WEB 215 a MAgl-glNE 2% KW/g! XEROPRINTER g H INVENTOR.

M m CHESTERF. CARLSON (210 255 BY 2 Fwldfiw ATTOR .E'Y

United States This invention relates to xerographic image fixing apparatus, and, particularly, to apparatus for effecting con tinuous vapor fixing of xerographic powder images.

The present application is a continuation-in-part of my co-pending application, Serial No. 299,673, filed July 18, 1952, now Patent No. 2,776,907; wherein certain of the subject matter of the present application is disclosed but not claimed.

In certain electrostatic recording processes, such as the electrophotographic, xerographic and electric printing processes described in my Patents 2,221,776, 2,297,691 and 2,357,809, and the process of graphic recording described in my Patent 2,624,652, an electrostatic image is developed by depositing a powder on a surface to produce a powder image. The powder image is then affixed to the surface upon which it has been deposited or on another surface to which it has been transferred. Heretofore, the usual method of fixing has been by the process of heat fusing, in which case the powder image must be formed of a thermo-adhesive material, such as a fusible resin, which becomes adhesive when heated.

While heat fusing has been put to practical use, certain difficulties have been encountered. Where the image is to be fused to paper, plastic or other organic base, as is usually the case, the powder must be made of material which becomes adhesive at a temperature below that which will cause damage, browning or distortion to the organic base. This imposes limitations on the choice of resins which make it difiicult to meet other desirable characteristics in the powder composition. Moreover, it has been diificult to reach an entirely satisfactory design of heat fuser with regard to short warm-up time, low electric current requirements, adequate heat insulation and uniform heat distribution.

Fixing of powder images by condensing a liquid solvent onto the image surface from a heated solvent vapor, as described, for example, in my above-mentioned Patent 2,624,652, has been successfully used and offers the advantages of a broadened choice of powder materials, lower power requirements, and elimination of heat damage to the base sheet. A device for fixing xerographic powder images by exposure to an atmosphere of solvent vapor at ambient temperature is disclosed in my co-pending application, Serial No. 554,006, filed December 19, 1955, now Patent No. 2,992,230. The latter device is currently in commercial use but is limited primarily to applications in which successive sheets are manually processed.

The present invention contemplates, as its principal object, improvements in apparatus for effecting continuous vapor fixing of xerographic powder images whereby powder images may be permanently fixed in high production installations with a minimum expenditure of electric power and solvent. In addition, the several structures of the invention are such to eliminate the need for a Warm-up period to condition the apparatus for normal operation. Furthermore, the apparatus of the invention eliminates the possibility of scorching the support surface on which xerographic powder images are formed, as may be done in heat fusing devices, and provides a preferred apparatus for fusing powder images on plastic film. These and other objects of the invention are attained by apparatus in which a continuous web of material, supportatent U ing continuous or successive xerographic powder images, is introduced into an atmosphere of solvent vapor which is at substantially the same temperature as the powder image, or lower. The vapor atmosphere is held at a vapor concentration sufiicient to produce absorption of solvent vapor by the powder image particles and consequent fusing of the image. absorption devices are included to retain the vapor solvent within the system, thereby minimizing loss of solvent and minimizing the possibility of introducing toxic or inflammable fumes from the solvent into the surrounding atmosphere. Other features of the invention will be apparent in the description of the invention.

Specific embodiments of the invention are disclosed in the accompanying drawings, in which:

FIGURE 1 is a plan view of a continuous vapor fixing device for use with an electrostatic powder printing or xerographic copying machine;

FIGURE 2 is a sectional view taken on the line 22 of FIGURE 1;

FIGURE 3 is a sectional view taken on the line 3-3 of FIGURE 1;

FIGURE 4 illustrates a modification of the invention in which a solvent absorbent chamber is added;

FIGURE 5 discloses a modified form of vapor fuser and solvent absorption unit of the type shown in FIG- URE 4;

FIGURE 6 is a diagrammatic view of a further modified form of vapor fuser that is particularly adapted for high speed operation;

FIGURE 7 is a diagram of the process steps that may be employed with the apparatus of FIGURES 4, 5 and 6;

FIGURE 8 discloses a high capacity fixing unit including means for recycling the solvent;

FIGURE 9 is a sectional view taken along the line 99 of FIGURE 8;

FIGURE 10 illustrates an electroprinting press incorporating fixing devices for fixing images on both sides of a web;

FIGURE 11 shows a further modification of a vapor fixing unit with means for solvent recovery;

FIGURE 12 is a schematic sectional view of a modified form of vapor fuser wherein the solvent vapor is continuously recycled and reused;

FIGURE 13 is a schematic sectional view of a modified form of vapor generating chamber for use with the powder image fusing apparatus of FIGURE 12.

FIGURES 1, 2 and 3 show a vapor fixing device for fusing a continuous web of copy issuing from an electrostatic powder printing machine or a continuous electrophotographic copying machine. Paper or plastic Web 30 carrying the unfixed powder images 31 enters in a horizontal plane from a powder printing or copying machine located at the left, as viewed in FIGURES 1 and 2, and passes over a horizontal roller 32 mounted in hearings on supports 33 and extending obliquely or diagonally across the web. The web then passes obliquely downward for a substantial distance to a point where it passes around and under a horizontal roller 34 mounted in bearings parallel to roller 32 and directly beneath it. The web then passes diagonally upward and around and over roller 32 again, this time at a spaced position on the length of roller 32 as clearly seen in the drawings, from which point it passes to a take-up reel 44 driven by motor 45 through constant tension clutch 46. It will be noted that the powder images are always kept on the outside of the web as it passes around rollers 32 and 34 In addition, recycling and/or wicking of fibreboard, fabric or blotting paper 37 and a solvent fountain bottle 38 maintains a shallow layer of liquid solvent 39 in the bottom of the tank by supply tube 40 to keep the wicking saturated.

' The top of the tank is closed in part by a central guide bar or plate 41 which is in contact with the inside face of the web entering and leaving the tank. A pair of adjustable plates 42 are mounted along the upper edges of the tank by screws 43 so that the inner edges of these plates can be adjusted to keep the entering and leaving slots at the minimum necessary to avoid contact with the image and still prevent excessive drag-out of vapor.

In operation of the fusing device of FIGURES 1, 2 and 3, the web 30 carrying the powder images is drawn through the device by the take-up reel 44, the web being kept under tension by the take-up reel and by a braking member on the supply reel in the printing or copying machine. As the web enters the vapor space 36 the powder image absorbs solvent vapor and becomes adhesive.

' When the web emerges the absorbed solvent rapidly evaporates and the images reach the take-up reel in dry condition. For high production machines a ventilating system-may be provided to remove vapor from the room.

Since substantially the only solvent consumed is that carried out of the tank by the resin image the fuser is very economical of solvent consumption and very little vapor is released into the room. An average powder image of text matter contains about one-twentieth of a gram or less of resin powder per square foot and an equal weight of solvent is sufiicient to cause fusion. It is obvious that the rate of solvent consumption, using cold vapor fusing, is very low. This has a marked advantage over heated vapor systems in which substantial quantities of solvent condense onto the entire web, whether an image is present or not, and must again be evaporated from the web. The evaporation of solvent from the liquid phase at a rate sufficient to maintain vapor saturation in space 36 can readily be provided by the conduction of heat inward through the chamber walls from the room. Evaporation of solvent into the vapor space lowers the temperature of the walls one or two degrees below room temperature causing the walls to absorb heat from the air around the tank.

FIGURE 4 shows a modification applicable to the apparatus of FIGURES l, 2. and 3 which provides the added feature of capture and absorption of solvent evaporated from the fused images. In this embodiment the fusing tank 35 is enclosed in an absorption tank 61 through which the web passes on entering and leaving tank 35'. Absorption tank 61 is provided with a removable cover 62 having a web opening provided with a guide bar 63 and side plates 64 similar to those in the top of the fusing tank. A liquid absorbent 65 fills the space in tank 61 around the sides of inner tank 35 and an overflow pipe 66 and drain valve 67 are provided and tapped into the side of absorbent tank 61 near its bottom. The open end of overflow pipe 66 is below the level of the top of inner tank 35 and insures that the absorbent liquid will not rise to a height where it can flow into the inner tank.

An absorbent liquid 65 is used which itself has low vapor pressure and which will readily absorb or dissolve large quantities of the solvent vapor used in inner tank 35 before the solvent vapor pressure from the mixture rises to a very high value. Thus, when trichloroethylene is used as a fusing solvent, the absorbent may be a high boiling petroleum fraction such as paraffin oil, new or used lubricating oils, and even oils containing a high percentage of dissolved waxes or tars, or crude petroleum with the volatile fractions removed. Suitable absorbent liquids for the volatile esters and alcohols include the higher boiling esters, alcohols, aliphatic oils, and some hydrocarbons.

In operation of FIGURE 4 the vapor space inside tank 35 is kept saturated with solvent vapor as previously described, while the space 68 above the absorbent liquid in outer tank 61 contains air in which the solvent vapor concentration is kept very low by the absorbent. As the web passes through inner tank 35 the powder images are fused with solvent vapor as previously described. Then as the ascending portion 69 of the web passes through air space 68 the solvent evaporates from the images so that they leave tank 61 in substantially dry and fixed condition. The solvent vapor released into space 68 is rapidly absorbed by the absorbent liquid thus keeping the vapor pressure of solvent in space 68 at a very low value which is most effective for drying the images. Absorption of solvent vapor by liquid 65 will gradually increase its voltime and the liquid level will rise in the outer tank. Should the level accidentally exceed the height of standpipe 66 the liquid will overflow through the pipe and prevent further rise of the level which might flood liquid over into inner tank 35. As solvent vapor is absorbed the concentration of dissolved solvent in the absorbent liquid 65 increases and consequently the vapor pressure of solvent in space 68 will gradually rise and decrease the thoroughness of the evaporation from the images. When the effectiveness of the absorbent liquid has been lowered to the point where adequate drying of the images no longer occurs it is replaced with fresh absorbent. As solvent vapor is absorbed by the absorbent liquid the latent heat of condensation of the solvent is imparted to the absorbent bath, thus raising its temperature slightly. Since the absorbent is in good heat exchange relation with the solvent in wicks 37 this heat is returned to the liquid solvent to compensate for its cooling due to evaporation of solvent into space 36.

FIGURE 5 illustrates another fixing device in which the web 30 is fed straight through in a horizontal plane. The web enters fusing tank It! through a horizontal slot defined by guide bar 71 and adjustable plate 72 and is provided with solvent vapor by solvent liquid 39 and wick member 73 inside the tank. Solvent tank is mounted inside the cover 74 of rectangular absorbent tank 75 and as the web 30 leaves the solvent tank it passes through a long shallow slot 76 into the air space above absorbent liquid.

Here the web passes between a pair of closely spaced horizontal electric hot plates or strip heaters 77 and 78 surrounded by layers of insulation 79 and 80 on all sides except the shallow space between them through which the paper web passes. The web and the fused images it carries are heated slightly by these plates to drive off the solvent more rapidly. The travel of the web sets up a circulation of air in the absorption chamber, as indicated by the arrows, which carries the slightly warm solvent vapor driven off from the web down over the surface of the absorbent liquid which rapidly takes up the solvent. The web leaves the absorption tank through an air seal comprising a soft rubber flap 81 which slides on the top surface of the web as the web rides over the horizontal guide flange $2 on leaving the tank. Some of the heat imparted to absorbent bath 65 is returned to liquid solvent 39 through the bottom of fusing tank 70 to thereby maintain the solvent temperature at a value which will maintain the required evaporation rate. Cooling fins 83 on tank 75 remove the extra heat imparted from the strip heaters. Most of the heat generated by the heaters is carried out by the paper web.

FIGURE 6 shows another form of straight-through fixing device especially suitable for high production speeds. As the web 30 passes horizontally from left to right, as shown, it passes first under a fusing head 84 where solvent vapor is blown against and along the web, and then the web passes under a drying head 85 where drying air is blown along its surface. Solvent vapor is generated in tank 86 containing liquid solvent 39 and having wicks 87 lining its walls. The vapor is drawn from the lower part of the vapor space through conduit 88 to the intake opening of blower 89 driven by electric motor 9%}. The output of the blower passes into a chamber 91 of the head 34- from which chamber it emerges through sloping slot 92 which projects the vapor stream against the top of the web 30. The vapor stream passes along the web to return slot 93 through which it passes into a chamber 94- and then through conduit 95 back to the top of tank 86. By providing a forced circulation of vapor the fusing process is accelerated. When the device is in continuous high speed use the rapid consumption of vapor by the web results in a lowering of temperature of solvent 39, thus tending to reduce the evaporation rate until the vapor concentration becomes too low to produce complete fixing of the powder images. A strip heater 108 is provided in tank 86 under control of thermostatic switch 109 to maintain an adequate evaporation rate under such high output conditions.

A similar system is provided for circulating drying air from absorption tank 96 through drying head 85. Air from the upper part of tank 96 is drawn under the horizontal flange 97 of floating intake nozzle 98 which is supported on floats 99 in order to route the air close to the surface of the absorbent liquid 65. The air passes up through conduit 100 to the intake part of blower 101 driven by motor 90. From the blower the air enters chamber 102 in head 85, then passes out of slot 103 and against the web, then along the web, through slot 104, chamber 105 and conduit 106 back to tank 96. A heater 107 mounted above the web in the air passage may be energized if desired to heat the web and hasten evaporation during drying.

FIGURE 7 is a diagram of a process cycle which may be used with FIGURES 4, 5 and 6, and an optional reclaiming cycle in which the solvent and absorbent are reclaimed by distillation of the spent absorbent bath. Where it is uneconomic to reclaim the materials the distillation steps can be eliminated and the spent absorbent liquid is thrown away. The heat introduced in the generation of the cold vapor is preferably obtained from the surroundings, or by transfer back from the absorbent tank, or from a thermostatically controlled heater and is sufficient only for vaporization of the solvent to produce a vapor at room temperature. The heat introduced in drying the web may come from the drying air at room temperature or may be supplied in part by an electric heater as described in connection with FIGURES 5 and 6. The temperature of the absorbent bath is raised slightly during operation and the heat passes out through the tank walls into the room, aided, if necessary, by added cooling surfaces on the tank in order that the bath temperature shall be held as low as possible.

FIGURES 8 and 9 show a high production unit such. as may be used to fix the output of a xeroprinting machine of the type shown on page 122 of Fortune Magazine (New York) for June 1949, or R. M. Schafiert Patent 2,576,047, for example. Web 138 of paper, cloth, sheet plastic or the like carrying a powder image or coating on its upper surface is led into the fixer over idle-r roller 139', and passes horizontally through the unit drawn by powerdriven delivery rolls 140, 141 at the output end. As it passes over roll 139 the Web enters a narrow lot or passage .142 which leads into the fixing chamber 143. Chamber 143 comprises a horizontal passage having a bottom wall 144 at the end where the web enters, and a bottom plate 145 joined to the inner end of wall 144 and extending to the output end of the unit, so that wall 144 and plate 145 form a continuous floor to the chamber 143. Wall 144 and the adjoining portion 165 of plate 145 are spaced slightly from the web but the rest of plate 145 is directly in contact with the web, and has a highly polished surface.

Above fixing chamber 143 is a return flow passage 146 separated by a horizontal partition 147 from fixing chamber 143 but communicating with it at the ends by openings 148 and 149. The top of passage 146 is enclosed by the top wall 150 of the unit and the sides and ends of 6 chamber 143 and passage 146 are closed by vertical side walls 151 and end walls 152.

An air blower 153 is located in passage 146 to withdraw air from fixing chamber 143 through opening 148 at the end at which the paper enters the fixing chamber and to return the air to chamber 143 through opening 149 at the web output end of the fixing chamber.

A series of heating elements 154, such as steam pipes or electric radiant heaters, are mounted beneath partition 147 in chamber 143 near the web output end, the elements being mounted across the chamber to afford uniform heating of all portions of the web width. Some of the elements 154 are also distributed across opening 149. Further heating elements 155 such as steam pipes or electric resistance elements, are provided inside bottom plate 145. Side walls 151 are covered with insulation layers 156 (FIGURE 9) to prevent condensation thereon. The entire unit maybe covered with insulation, if desired.

A box-like housing 157 is provided at the web output end of the unit, having a common wall 152a with the end of chamber 143 and passage 146, and has an exhaust pipe 158 connected thereto provided with exhaust blower 159.

Common wall 152a is provided with a flexible flap 160 of thin sheet metal, leather, plastic or rubber which rests lightly on top of web 138 where it leaves the fixing cham. her, and thereby acts as an air seal.

A liquid solvent feed pipe 161 provided with needle valve 162 supplies liquid solvent to drip tube 163 located in passage '146 above that portion of partition 147 which is over heating elements 154 and consequently is at an elevated temperature. The edges of the heated area of partition 147 are formed into a ridge 164 enclosing the area to retain any excess liquid which may accumulate, although the solvent which drips from tube 163 will ordinarily evaporate before it can spread to the edge of the area.

In operation of the unit of FIGURES 8 and 9 the web 138 is started through the unit so that it is grasped by delivery rollers 140, 141 which will then continuously draw the web through the fixing chamber. Elements 154 and 155 are supplied with a heating medium and blower 153 is operated to circulate the air in the unit in a closed path through passage 146, opening 149, fixing chamber 143, and opening 148 back into passage 146. The air thus enters chamber 143 at the end where it is first heated by elements 154 located across opening 149 and then passes under partition 147 where it is further heated by the elements 154 located under the partition. In the heated zone the air also comes into contact with web 138 and passes over it in counter-flow relation throughout the heated zone and then into an unheated zone near the end of chamber 143 at which web 138 enters. Valve 162 is adjusted to provide a drip feed of liquid solvent having relatively low vapor pressure at room temperature and a high vapor pressure at the temperature reached by the air in the heated zone.

The web, on entering the fixing chamber is at substantially room temperature and hence solvent vapor from the solvent-laden air coming from the heated zone rapidly condenses on the web and any powder image it carries on its surface. The powder is dissolved or rendered adhesive by the condensed solvent and becomes bonded to the web. Condensation of vapor raises the temperature of the web so that the rate of condensation slows down as the web advances through the unheated zone. As the web approaches the heated zone a point of equilibrium is reached so that condensation ceases and then the condensed solvent begins to evaporate under the combined influence of the heated air stream and heat radiated from elements 154 and from plate 145. The air stream, having been partly denuded of solvent vapor as it passed over the relatively cold web, and returned through passage 146 to the heated zone readily dries out the now heated web of the solvent it has previously condensed so that the web leaves the fixing chamber in a substantially solventfree state. Most of the solvent never leaves the fixing chamber since it is condensed on the web at the cold end of the chamber, again evaporated as the web moves to the heated zone and returned to the cold end by the air stream. Drip tube 163 introduces additional solvent into the air stream only to compensate for that small amount which remains in the web and is carried out of the chamber and any which may be carried out by moving air. Since the chamber is substantially sealed against air leakage there is negligible loss from this cause. Housing 157 and exhaust pipe 153 are primarily for safe removal of small amounts of solvent from the web as it leaves the unit in case of unusual conditions. Since the powder image has been fixed before it leaves the fixing chamber the sliding flap 160 can do no damage to it and prevents the web from carrying an air layer out of the unit. Practically no vapor reaches the back of the web and the operation is so rapid that the condensed solvent will not normally penetrate through the web. The recessed portion 165 of plate 145 further insures that no contact will be made with the web until the solvent has been largely driven off in the case of thin webs where solvent penetration might occasionally take place. This insures that there will be no smudging of any image which might be on the back of the web.

FIGURE illustrates the invention applied to an electroprinting system for printing on both sides of a web. A web 167 (of paper, for example) is fed from supply roll 166 through an electroprinting machine 168, such as the machine described in the aforementioned Fortune Magazine article, or in Schaffert Patent 2,576,047, Where a powder image is applied to its upper face. The web 167 then passes through a fixing unit 169, similar to that illustrated in FIGURES 8 and 9, where the image is affixed to the web. On leaving rolls 140, 141 of unit 169 the web passes down and under an idling roller 170 which it leaves in a horizontal path with its unprinted face upward. The web then passes through another electroprinting machine 171 where a powder image is applied to its now top surface, after which the web proceeds through a second fixing unit 172 to fix the second image.

FIGURE 11 shows a further type of fixing unit intended primarily for use with heavy vapors and moderate web speeds. The unit comprises a vapor tank 173 having a closed bottom and sides and heated at the bottom by a hot plate 174 or other form of heating element. A layer of liquid solvent 175' is placed in the bottom, a solvent being selected which will yield a vapor substantially above the density of air and preferably several times the density of air. A vapor level control channel 176 is provided around the upper portion of the side walls. This comprises a recess running horizontally around the tank with its walls forming a trough. A pipe 177 carrying cold water or other cooling fluid is laid in the trough and openings 178 are provided to allow condensed vapor to run into the tank. When heated by element 174 the solvent forms a heavy vapor layer 179 up to the level of the channel 176, as shown. The upper parts of the side walls of the tank are sloped inward to form a throat portion 182 in which is mounted a hot plate 180 whose back is enclosed by a heat shield 181.

The back of the heat shield and the face of the hot plate are spaced from the walls of the throat 182 to leave narrow slots 183 and 184, respectively, through which a Web of paper or other material can pass into and out of the tank. Web guide rollers 185 and 186 are mounted above slots 183 and 184, respectively, and a larger roller or drum 187 is located inside the vapor zone of the tank so that a web 188 can be fed through the tank by passing it over roller 185, down through slot 183, around drum 187, up through slot 184, and over roller 186.

Hot plate 180 is heated by embedded heating elements 189 which may be steam pipes or electric resistance elements. A cold plate 190 is mounted on the top edge ofthe tank throat 182 on the side facing the hot plate and is parallel with the face of the hot plate, so that the space between them comprises an upward extension of slot 184. Cold plate 190 is provided with cooling pipes 191 through which cold water or a refrigerant is circulated. Hot plate 180 extends down into the tank below the throat and a series of baffles 192 are mounted in the tank adjacent to the hot plate surface and sloping away from it.

In operation the web 188 carrying a powder image is drawn through the tank in the path described. The powder image is located on its upper or outside face as the web passes over roller 185. As the web enters the tank the shield 181 protects it from heating by the hot plate so that the web is relatively cold as it enters the vapor zone. Solvent condenses on the web and powder image as it passes through the vapor and passes underneath drum 187, thus making the image adhere to the web. As the web advances up into contact with the lower portion of the hot plate and out of the vapor zone it becomes heated and most of the solvent is re-evaporated in the region of baffles 192 which deflect the vapor away from the web and allow it to settle back to the vapor zone along the wall of the tank. When the web reaches slot 184 and passes between the hot plate and cold plate 190 it is subjected to a condition in which the heat drives 011 any remaining solvent and the resulting vapor is immediately condensed on the cold plate so that the vapor concentration in the slot is kept at a minimum. The condensed solvent on the cold plate drains back down the wall to the bottom of the tank. This affords a very effective fixing operation with substantially no loss of solvent.

Besides making possible the use of powders which are not fusible by heat, the solvent fixing means described also afford economies in heat utilization which are particularly valuable in large production units, such as those illustrated in FIGURES 8 to 11. In the unit of FIGURE 8, for example, the only heat drain on the system, except for losses through the walls, is that required to heat the web from room temperature to substantially the solvent boiling point, which may be in the order of C. If a heat fusion method were used it would be necessary with most suitable powders to raise the temperature of the web above or 200 C. In addition to the extra B.t.u. output required the heat must be supplied at a higher temperature, making economical heat sources, such as steam pipes, unavailable.

Very little solvent is required in order to fix a resinous powder image and the web of paper or other material remains relatively dry. The solvent also lowers the melting or softening point of the powder composition so that it is sometimes possible to limit the solvent condensation to a very small amount and rely upon the final heating step to further the softening of the powder to its adhesive point before complete evaporation of the solvent occurs. It is thus possible to obtain fixing under conditions in which either the temperature or the solvent alone would be inadequate.

It is apparent that a wide variety of powder images can be fixed by use of the present invention, it being only necessary to use a solvent which dissolves or renders adhesive the particular material of which the powder is composed. On the other hand it is also possible to provide a web which is rendered adhesive by the solvent, in which case the powder need not be solvent-fusible. In some cases, as where the web is of plastic film, such as ethyl cellulose or nitrocellulose, its surface can be rendered adhesive by a solvent such as butyl lactate, to permit the film to adhere to or embed the powder image. In other cases the web may have a coating of an adhesive film which is made to adhere to the powder image. For instance, paper with an ethyl cellulose or a polyethylene coating can be made to adhere to and fix a carbon or lampblack image.

Soluble powder images may be formed of a wide variety of materials, such as finely divided resin, Vinsol, ethyl cellulose, asphalt, sodium carboxymethylcellulose, Amberol F-71, polystyrene, or zein. (Vinsol is a petroleum hydrocarbon-insoluble resin derived from pine wood, and produced by Hercules Powder Company, Wilmington, Delaware. Amberol F-71 is a resin-modified phenolformaldehyde resin manufactured by Rohm and Haas Company, Philadelphia, Penna.) The powders may be dyed or pigmented.

While low boiling solvents such as ethyl alcohol, water and naphtha may in some cases be used with cold webs, it is usually preferable to use a solvent of medium or high boiling point, such as butanol (butyl alcohol), butyl lactate, butyl acetate, amyl acetate, octyl alcohol, butyl cellosolve, carbitol, diothyl carbitol, butyl carbitol, carbitol acetate, butyl carbitol acetate, trichloroethylene and perchloroethylene.

Examples of solvents useful with specific powders are:

For Vinsol-ethyl alcohol, butyl alcohol, butyl cellosolve.

For ethyl cellulose or polystyrene-butyl acetate, trichloroethylene.

For asphalt-perchlorethylene.

For sodium carboxymethylcellulose-water.

For zein90% ethyl alcohol.

For Arnberol F-7 ltrichloroethylene, perchlorethylene.

For high speed operation, with the forms of the invention shown in FIGURES 8 to 11, it is desirable to re-gulate the heating of the solvent to raise it to a temperature at which it has a substantial vapor pressure but to keep the temperature below the boiling point. With perchlorethylene, for example, which has a boiling point of 121 degrees C., excellent fixing of Amberol images can be accomplished in a vapor chamber at 80 to 100 degrees C.

In any event it is apparent that the partial pressure of the solvent in the chamber is greater than the vapor pressure of the solvent from a tacky solution of the soluble resin at the temperature of the entering web of sheet material so that solvent will condense on and tackify the resin powder or coating.

FIGURE 12 discloses an improved continuous vapor fusing apparatus that is particularly adapted for fusing xerographic powder images onto webs of paper, plastic film material, and the like, in relatively high production intermittent operation. In this arrangement, a web 210 carrying powder image 211 emerges from xerographic machine 212 and is pulled straight through the fuser by web advance rollers 213. At the entrance slot to the fuser is a swinging flap or door 214 which drops down and closes the slot to reduce vapor loss when the machine is shut down. An electromagnet 215 pulls the door 214 up to open the slot whenever the operating switch for the drive motor 238 for advance rollers 213 is turned on. This will usually be the same switch as starts the xerographic machine.

A vapor generating chamber 216 is located in the upper part of the fuser housing and consists of a vertical channel lined with wicking 217 which dips into a solvent reservoir 218 where solvent liquid is maintained at a constant level by feed bottle 219'. Solvent vapor can pass down through outlet passage to vapor fusing zone 221 where it comes into contact with the powder image 211 on web 210 as the web passes through the fuser from left to right.

As the web continues its travel from fusing zone 221 it passes first through a passage 222 where the solvent condensed on the image has time to penetrate through the image powder and bond it to the web. It then passes between a pair of heated platens 223 and 224 where the solvent is vaporized again and driven off the web and the now-fused resin powder image. Platen 223 is closely spaced above the web but out of contact with it, while platen 224 contacts the lower face of the web. Platen 224 extends to the right end of the fuser and is covered with heat insulating layer 225 on its lower surface.

The vapor which is driven off the web and image in zone 226 between the platens adds to the volume of gas and hence there is an expansion continually taking place from this zone. Part of the vapor may flow to the left, as shown by the arrow, in counterfiow relation to the web travel, and condense on an approaching section of the image if it still can absorb further solvent. The major part of the vapor as well as accompanying air will drift to the right due to the drag of the web on the air and vapor, and will pass upward to the right of platen 223. Very little, if any, vapor will be carried out with the web, however, because a flexible flap 227 closes the exit slot and drags against the top of the web. Flap 227 is of heat resistant flexible material such as Teflon or Neoprene. If desired, a series of flaps can be provided to produce multiple seals.

The heated vapor and air which leaves the zone 226 and passes up around the right edge of platen 223 can return to the fusing zone 221 directly through passage 228, or via cooling passage 229 to the top of vapor generating chamber 216. An adjustable gate 230; controlled by manual lever 231 can be set at any position to divide the flow between passages 228 and 229 in any proportions. Cooling passage 229 has cooling fins 232 on its exterior, and a fan 233 is preferably arranged to circulate room air around the fins to lower the temperature of the air and vapor circulating through passage 229 toward room temperature.

The cooling step is of importance in maintaining satisfactory operation. Since very little solvent ever leaves the fuser it will be seen that if more vapor were continually added by generating chamber 216- a point would eventually be reached where the air would become oversaturated in every place but the hottest zone and vapor condensation would begin to take place on the walls, as well as excessive condensation on the entering web. By pre-cooling the air and vapor in passage 229 it is unable to pick up any more vapor in chamber 216 than it can hold in the cooled state, so the system never becomes overcharged with vapor. Only enough vapor is added to the air as it passes through chamber 216 to replenish the small amount of solvent which is dragged out with the web or which leaks out of the entrance slot, and there will be no vapor condensation on the walls.

There may, however, be some moisture condensation, if the web contains moisture as it enters the fuser. The heated platens will drive off some or all of the moisture from the web and as water vapor accumulates in the fuser it will condense on the walls. To remove condensed moisture the walls are provided with gutters 234 and drain tubes 235 which carry condensed moisture to the drip pan 236 at the bottom of the fuser, where it drains out through vapor seal tube 237.

It is preferred that gate 230 be set to provide the minimum flow through the vapor generator that will maintain the required vapor concentration, the rest of the flow being by-passed through passage 228.

Heating platens 223 and 224, as well as blower 233 and electromagnet 215, are connected to the same power circuit as web advance motor 238, and this can be controlled. by the starting switch 241 for Xerographic machine 212. Vapor generator 216 keeps the fusing zone 221 supplied with saturated vapor even when the machine is shut down and cold, ready to start fusing copy immediately. By lifting flap 227, so it doesnt drag on the web for a short time at the start of operation the fused copy will become air dried as soon as it leaves the fuser. When the platens have warmed up the flap can be lowered onto the web surface since the images will be dry and nonsmearing as they leave the fuser. It is also contemplated that the platens can be kept warm by a low wattage standby current and switched to a higher wattage circuit when operation begins.

Suitable solvents are trichloroethylene, perchlorethylene, and certain Freons. Trichloroethylene has a boiling point of 87 C. Platens 223 and 224 may be operated at a temperature of to 200 C. and the web surface carrying the image may be raised to 90 to 100 C. during the drying step. The wattage required is much less than that needed for heat fusing of present xerographic toners. Also, since the web is not heated above 100 some of the moisture contained in the paper, if paper is used, will not necessarily be driven off but will remain in the final copy. This reduces paper deterioration. In the case of plastic films the temperature of the platens can be even lower since a surface removal of solvent is all that is required and the film is never subjected to temperature which will harm or distort it.

The air and vapor which passes through passage 229 is preferably cooled to 50 C. or below. At 50 C. the vapor pressure of trichloroethylene is only around 220 mm. of mercury and hence this is the maximum vapor concentration (partial pressure of the solvent vapor) which will be reached in the fuser.

When the fuser cools, after use, the vapor pressure of the trichloroethylene will become still lower and there will be some condensation on the walls. The resulting liquid will drain out of the fuser into collecting bottle 239 along with the moisture. Since it is heavier than water it will form a layer under the water, which protects it from evaporation and it can later be separated by drain valve 240 and returned to the bottle 219.

It should also be noted that the hot vapor returning via passage 228, when it condenses on the image, will add its thermal heat and heat of vaporization to the image and raise the temperature of the image even before it passes under the platens. This reduces the amount of heat which the platens are required to supply to the image by direct radiation and speeds up the drying step.

In FIGURE 13 there is disclosed a modified form of vapor generating chamber that is adapted to function in conjunction with the powder image fusing apparatus of FIGURE 12, and is particularly adapted for applications in which the fusing apparatus is required to be shut down or maintained in standby condition for long periods of time. For simplicity of illustration, the vapor generating apparatus of this modification is shown independently of the remainder of the fusing apparatus. It is to be understood that this equipment is adapted to function with a fusing and recirculating apparatus of the type shown in FIGURE 12, wherein corresponding elements are identified by the same reference characters.

In this arrangement, vapor generating chamber 316 is located in the upper part of the fusing housing and comprises a horizontal reservoir of liquid solvent 318 whose level is maintained by a feed bottle 319. Partitions 321 serve to guide the air coming from coating passage 229 against the surface of the liquid, after which it passes up over wall 323 and down through outlet passage 320 to vapor fusing zone 221.

A small electric blower 322 in passage 320 may be energized by operating switch 324, if necessary, to increase the rate of vapor addition to the system.

This arrangement has an advantage over that disclosed in FIGURE 12 for applications in which the machine is required to be shut down or maintained in standby condition for long periods, as the rate of vaporization from the vapor chamber is lower when there is no air fiow taking place. A layer of heat insulation 325 also cuts down the rate of heat transfer from the exterior of the vapor chamber, hence reduces evaporation. However, when air flow begins, vaporization readily takes place from the liquid to the warmer air coming from passage 229.

It may be noted that several forms of the invent-ion have been described as applicable for fixing or fusing xerographic powder images on continuous web materials such as paper, plastic film, or the like. However, it is to be understood that the invention is not limited in its application to use with continuous web material. Obviously, in the forms of the invention shown in FIGURES 5, 6, 12 and 13, the continuous web material illustrated in each instance may be replaced by an endless belt formed of metallic foil or other substance having high heat-conducting characteristics, whereby it may be employed as a conveyor belt for supporting and transporting successive 5 sheets of support material having xerographic powder images thereon through the respective vapor fusing apparatus.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A continuous vapor fuser for fixing fusible powder images onto sheet material, said fuser comprising walls defining a substantially closed vapor chamber with a web inlet opening and a web outlet opening in said walls,

web conveying and support means to advance a web in a path through said chamber from said inlet opening to said outlet opening,

one of said walls at said inlet opening being spaced from one surface of said web to provide clearance for powder image carried on said web,

sealing means at said outlet opening in position to bear against both surfaces of said web to prevent free vapor discharge at said outlet, and a heater in close proximity to said web and adjacent said outlet opening to vaporize solvent from said web and image, the area within said vapor chamber and adjacent said inlet opening being free of any heating means to enable return vapors to condense upon said web in the vicinity of said inlet opening,

said walls also providing a vapor passage to return said vaporized solvent toward said inlet opening into contact with said web and image in the region of said inlet opening.

2. A continuous vapor fuser for fixing fusible powder images onto sheet material, said fuser comprising walls defining a substantially closed vapor chamber with a web inlet opening and a web outlet opening in said walls,

web conveying and support means to advance a web in a path through said chamber from said inlet opening to said outlet opening,

one of said walls at said inlet opening being spaced from one surface of said web to provide clearance for a powder image carried on said web,

sealing means at said outlet opening in position to bear against both surfaces of said web to prevent free vapor discharge at said outlet, and a heater in close proximity to said web and adjacent said outlet opening to vaporize solvent from said web and image, the area within said vapor chamber and adjacent said inlet opening being free of any heating means to enable return vapors to condense upon said web in the vicinity of said inlet opening,

said walls also providing a vapor passage to return said vaporized solvent toward said inlet opening into contact with said web and image in the region of said inlet opening,

and means for supplying additional solvent vapor to said chamber to compensate for solvent dragged out of said chamber by said web.

3. A device for affixing xerographic powder images to a web of sheet material, the powder comprising said 65 images including a soluble component,

which device comprises walls defining a substantially enclosed space having an entrance slot and an outlet slot for passage of a web through said space,

heating means within said space and adjacent said outlet slot for vaporizing solvent into said space from said powder image and web, the area within said space and adjacent said entrance slot being free of any heating means,

and said walls constituting means to convey the vaporized solvent into contact with the relatively cooler 13 area of said web adjacent said entrance slot, whereby to condense said vapor on the entering web in the vicinity of said entrance slot.

4. A device as claimed in claim 3 in which solvent vapor moving means are provided to circulate air and 5 solvent vapor which has been vaporized into said space by said heating means into contact with an area of the entering web adjacent said entrance slot, whereby to condense said vapor on said entering web, and to circulate solvent-depleted air from the area of the entrance slot into 10 contact with said web area adjacent said outlet slot.

References Cited in the file of this patent UNITED STATES PATENTS 1,228,225 Lynah May 29, 1917 15 14 Motley Feb. 4, 1930 Freeland Feb. 6, 1934 Lydon July 28, 1936 Benner et a1 Sept. 6, 1938 Hershberger Nov. 29, 1938 Bosomworth et al. Jan. 28, 1947 Long June 20, 1948 Derby Oct. 25, 1949 Dungler June 29, 1954 Mayo July 20, 1954 Greaves Dec. 6, 1955 FOREIGN PATENTS France May 23, 1938 

1. A CONTINUOUS VAPOR FUSER FOR FIXING FUSIBLE POWDER IMAGES ONTO SHEET MATERIAL, SAID FUSER COMPRISING WALLS DEFINING A SUBSTANTIALLY CLOSED VAPOR CHAMBER WITH A WEB INLET OPENING AND A WEB OUTLET OPENING IN SAID WALLS, WEB CONVEYING AND SUPPORT MEANS TO ADVANCE A WEB IN A PATH THROUGH SAID CHAMBER FROM SAID INLET OPENING TO SAID OUTLET OPENING, ONE OF SAID WALLS AT SAID INLET OPENING BEING SPACED FROM ONE SURFACE OF SAID WEB TO PROVIDE CLEARANCE FOR POWDER IMAGE CARRIED ON SAID WEB, SEALING MEANS AT SAID OUTLET OPENING IN POSITION TO BEAR AGAINST BOTH SURFACES OF SAID WEB TO PREVENT FREE VAPOR DISCHARGE AT SAID OUTLET, AND A HEATER IN CLOSE PROXIMITY TO SAID WEB AND ADJACENT SAID OUTLET OPENING TO VAPORIZE SOLVENT FROM SAID WEB AND IMAGE, THE AREA WITHIN SAID VAPOR CHAMBER AND ADJACENT SAID INLET OPENING BEING FREE OF ANY HEATING MEANS TO ENABLE RETURN VAPORS TO CONDENSE UPON SAID WEB IN THE VICINITY OF SAID INLET OPENING, SAID WALLS ALSO PROVIDING A VAPOR PASSAGE TO RETURN SAID VAPORIZED SOLVENT TOWARD SAID INLET OPENING INTO CONTACT WITH SAID WEB AND IMAGE IN THE REGION OF SAID INLET OPENING. 